Productive varicella-zoster virus (VZV) infection of the central nervous system (CNS) was demonstrated in 11 acquired immune deficiency syndrome (AIDS) patients using immunocytochemistry and in situ hybridization. A characteristic zoster skin eruption was seen in only four cases. From our own series and 11 other cases in the literature, we identified five clinico-pathological patterns of VZV infection of the CNS in AIDS patients which could occur simultaneously. (i) Multifocal encephalitis predominantly involving the white matter, likely to be due to haematogenous spread of the infection was found in four cases. (ii) Ventriculitis was found in three cases. In two cases there was complete acute or chronic necrosis of the ventricular wall with marked vasculitis; in the third, the ependymal lining appeared irregular with foci of VZV-infected ependymal cells, some of which protruded into the ventricular lumen. (iii) Acute haemorrhagic meningo-myeloradiculitis with necrotizing vasculitis was observed in two cases. In one, this was associated with ventriculitis and was possibly due to shedding of infected ependymal cells into the ventricular lumen and secondary seeding of the CSF. (iv) Focal necrotizing myelitis was seen in one case. It followed cutaneous herpes zoster and was considered to result from neural spread from the diseased dorsal root ganglion similar to cases previously described of encephalitis limited to the visual system following VZV ophthalmicus, or bulbar encephalitis following a trigeminal zoster. (v) Vasculopathy involving leptomeningeal arteries and causing cerebral infarcts was seen in four cases, it was associated with meningitis in most cases. These findings are in keeping with the observation in non-AIDS patients that VZV spread to the CNS may follow different routes. Our study tends to show that VZV infection of the CNS occurs more frequently in AIDS than previously suspected and suggests that it must be considered as a diagnosis in cases of encephalitis, ventriculitis, focal myelitis, acute myeloradiculitis and cerebral infarcts in these patients.